Voltage-regulator circuit



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Mia-H 11, 1958 w. J. HEAcocK, JR 2,826,735

VOLTAGE-REGULATOR CIRCUIT 2 Sheets-Sheet 2 Filed Aug. 24, 1955 vor'rAGE-nnoULAToR CIRCUIT William J. Heacock, Jr., Levittown, N. Y., assignor to Hazeltine Research, Inc., Chicago, Ill., a corporation o illinois Application August 24, 1955, Serial No. 530,334

7 Claims. (Cl. 323-22) General v This invention relates to voltage-regulator circuits for supplying a constant magnitude direct-current voltage to a load and, particularly, to such voltage-regulator circuits which have both a high degree of direct-current stability and a high degree of alternating-current stability.

lt has been heretofore proposed to provide a voltageregulator circuit which utilizes an electron-discharge tube to adjust the magnitude of a direct-current voltage supplied to a load and an amplifier circuit which is responsive to variations in the voltage supplied to the load for controlling the conductivity of the electron tube to cornpensate for any Voltage variations. In order to provide a high degree of direct-current stability it is necessary that the amplier portion of the voltage-regulator circuit have a rather large amount oi gain. When a large amount of gain is provided, however, the tendency of the closed loop feed-back circuit formed by the electron tube and the amplilier to oscillate is greatly increased. This tendency to oscillate is indicative or poor alternating-current stability and is particularly troublesome where, from time to time, the current drawn by the load undergoes sharp transient variations. This is because such transient variations contain high-frequency components which may serve to initiate either a transient or a sustained self-oscillation of the feed-back circuit of the voltage regulator.

It is an object of the invention, therefore, to provide a new and improved voltage-regulator circuit having both a high degree of direct-current stability and a high degree of alternating-current stability and which is not readily susceptible to self-oscillation.

In accordance with the invention, a voltage-regulator circuit for supplying a constant magnitude direct-current voltage to a load and normally having circuit capacitance coupled across the output terminals thereof which tends to cause the voltage-regulator circuit to oscillate comprises supply circuit means for supplying a direct-current voltage and an electron-discharge device for adjusting the magnitude of the direct-current voltage supplied to the load. The voltage-regulator circuit also includes ainpliier circuit means responsive to variations in the magnitude of the voltage supplied to the load for controlling the operation of the electron-discharge device to compensate for such voltage variations. The Voltage-regulatorl circuit further includes iirst impedance means for isolating the closed loop feed-back circuit formed by the electron-discharge device and the amplier circuit means from the circuit capacitance for minimizing undesired high-frequency phase shift introduced thereby which tends to cause this closed loop feed-back circuit to undergo high-frequency oscillation. Additionally, the voltageregulator circuit includes second impedance means for luy-passing the first impedance means for enabling normal operation of the voltage-regulator circuit for the lower frequency components of the load current variations.

For a better understanding of the present invention, together with other and further objects thereof, reference is nited States Patent O f 2,826,735 Patented Mar. 11, 1958 had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings:

Fig. l is a circuit diagram, partly schematic, of a conventional Voltage-regulator circuit of the series type;

Fig. la is an alternating-current equivalent circuit diagram for the voltage-regulator circuit of Fig. l;

Fig. 1b is a vector diagram used in explaining the operation of the voltage-regulator circuit of Fig. l;

Fig. 2 is a circuit diagram, partly schematic, of a seriestype voltage-regulator circuit constructed in accordance with the present invention;

Fig. 2a is an alternating-current equivalent circuit diagram of the voltage-regulator circuit of Fig. 2 for the higher operating frequencies;

Fig. 2b is a vector diagram used in explaining the operation of the voltage-regulator circuit of Fig. 2;

Fig. 3 is a circuit diagram, partly schematic, of a shunttype voltage-regulator circuit constructed in accordance with the present invention, and

Fig. 4 is a circuit diagram of an alternate form or" compensating network which may be utilized in the Figs. 2 and 3 voltage-regulator circuits.

Description and operation of conventional voltageregulator circuit of Fig. 1

Referring to Fig. l of the drawings, there is shown a conventional form of voltage-regulator circuit of the series type. The voltage regulator there shown includes an alternating-current source 16 coupled in cascade with a rectifier 11 and a smoothing iilter i2, these three units acting in conjunction with one another to supply an unregulated direct-current voltage at the output terminals of the filter 12. rihis unregulated direct-current voltage is, in turn, supplied to a load i3 by way of the intermediate circuits which serve to regulate this direct-current voltage so that the magnitude of the voltage supplied to the load 13 is maintained constant in spite of any variations in the current drawn by the load 13 or in spite or" any uctuations in the magnitude of the alternating current supplied by the source 10.

The voltage-regulator circuit includes a series-regulator tube 14, which may be of the conventional triode type, and an amplifier circuit 15 which is coupled between the output electrode of the tube i4, in this case the cathode 16, and the control electrode 17 of the tube 14. The voltage-regulator circuit also includes a high-frequency lay-pass condenser C and a source of voltage reference potential as represented by the battery T he ampliiier 15 serves to compare the voltage level at an output terminal 21 of the voltage-regulator circuit with the voltage supplied by the voltage reference source 2li so as to supply a signal representative of the ditlference between these two voltages to the control electrode i7 of the tube 14. In this manner, if the magnitude of the voltage at the output terminal 2li deviates from its desired constant value, then the signal supplied by the amplier l5 to the control electrode 17 is or" such magnitude and polarity as to change the conductivity of the tube 14 so as to oppose the change in the magnitude of the voltage at the output terminal 2l.

Where a high degree of direct-current stability is required of the voltage-regulator circuit, it is necessary that the amplier 15 have a large gain factor. This enables the amplifier 15 to be very sensitive to any change in the magnitude of the output voltage at the terminal 21 and hence enables the voltage-regulator circuit to hold this output voltage very close to the desired operating value. To this end, the amplier 15 may include several stages of amplification, As mentioned, however,

- where the gain of the amplier la' is very high, the tendwhere gm is the transconductance factor of the tube 14. Also, the load 13 has been represented diagrammaticaliy by an equivalent impedance ZL. lt will thus be noticed from the Fig. la diagram that the signal at the output of the amplifier l is fed bach by way of a feed-back path including the equivalent resistor R to the input ternnnals of the amplifier For the higher frequency range, which is the range of particular interest, the reactance of the by-pass condenser C is small compared to the resistance or" the load ZL and hence, for present purposes, the presence of the load ZL may be ignored. -ln this manner, the current flowing through the feedback path passes through both the resistor R and the condenser C, which means that there is a substantial shift in phase between the voltage signal at the output terminals of the amplifie" "ad and the voltage signal fed back to the input terminals of the amplifier 15.

This phase shift may be more readily understood oy reference to the vector diagram of Fig. lb. Thus, assuming a feed-bach current to be owing through the feednach path including the resistor R andthe condenser C, then a voltage drop VR is developed across the equivalent resistor R while a voltage drop VC is developed across the condenser C. The resultant of these two voltage drops is denoted by the vector VT and represents the voltage signal at the output terminals of the amplifier 15. As is apparent, the voltage signal at the amplifier i5 input is denoted by the vector VC which lags the amplifier 15 output voltage VT by a phase angle 0.

For direct-current and low-frequency signal variations, the amplifier 15, in addition to amplifying any signal variation translated thereby, is also effective to invert the polarity of such signal variations; In other words, the signal supplied at the output terminals of the amplier .i5 after translation thereby is 180 out of phase with such signal as originally supplied to the input terminals of amplifier l5'. Assuming no phase shift in the` feed-back path including the equivalent resistor R, this, then, is the required condition for negative or degenerative feed-back operation. Such operation does, infact, occur over the lower frequency range because the reactance of condenser C is large and, hence, the voltage signal VC which is fed back to the amplifier 15 input is very nearly in phase with Athe output voltage signal VT. At higher frequencies, however, more of the feed-back signal is developed across the resistor R while less is developed across the condenser C. This is because the reactance of the condenser C decreases as the frequency increases. Thus, at some high frequency the feed-back signal component VC at the .input to th-e amplifier 2.5 is going to be very nearly 90 out of phase with the feed-back component VT .at the output of the amplifier 15. This 90 phase shift together with the phase shifts which normally occur within the amplifier 15 at these frequencies will be sufficiently great so as to cause positive or regenerative feed-back operation to occur. When this occurs, lthe closed loop feed-back circuit will oscillate. This self-oscillation is of course highly undesirable in a voltage-regulator circuit which is intended to supply a constant magnitude direct-current signal to th load 13.

From the foregoing, it is apparent that `the phase shift caused by the by-pass condenser C, which is connected directly across the output terminals 21, 22 of the voltageregulator circuit, is effective at higher frequencies t-o cause self-oscillation of the voltage-regulator circuit. This bypass condenser C, however, must be present in order that the Voltage-regulator circuit may have a very low output impedance over the higher frequency range. Otherwise, the output impedance of the regulator circuit, which is common to all Athe multistage circuits which make up the load i3, would cause undesirable interstage coupling between such load circuits.

Description of voltage-regulator circuit of Fig. 2

Referring now to Fig. 2 of the drawings, there is shown a series-type voltage-regulator circuit, constructed in accordance with the present invention, for supplying a consta-nt i. agnitude direct-current voltage to the load 13 and normally having circuit capacitance as represented, for example, by the condenser C coupled across the output terminals 21, 2.2 thereof which tends to cause the voltageregulator circuit to oscillate. Parts of the voltage-regulat-or circuit of Fig. 2 are similar to corresponding parts of the voltage-regulator circuit of Fig. l and accordingly the same reference numerals have been used for corresponding elements in the two figures.

Considering the voltage-regulator circuit of Fig. 2, such circuit includes supply circuit means for supplying a direct-current voltage. This supply circuit means may include, for example, the alternating-current source 10 coupled in cascade with the rectilier il and the filter l2. The voltage-regulator circuit of Fig. 2 also includes an electron-discharge device 14 having a cathode 16, acontrol electrode 1.7, and an anode 19 for adjusting the magnitude of the direct-current voltage supplied to the load 13. For the yseries-type regulator shown in Fig. 2, the electron-discharge device or tube i4 is connected such that the anode 19 to cathode 1.6 discharge path thereof is coupled in series between the supply circuit means `and a rst one of the output terminals 2l, 22 of the voltageregulator circuit.

C Additionally, the voltage-regulator circuit constructed 1an accordance with the present invention includes ampliner circuit means l5 responsive to variations in the magnitude of the voltage supplied to thc load rfor trolling the operation of the electron-discharge device to compensate for such voltage variations. Vthe case of the series-type voltage regulator shown F 2, the amplifier circuit means is coupled between theu control electrode 1.7 of the tube 14 and the nrst-mentioned output terminal Zi of the voltage-regt or circuit, the coupling Vto the output terminal 21 being by way of a compensating network 30 which will be discussed presently. A

n The voltage-regulator circuit of Fig. 2 further includes nrst impedance means for isolating the closed loop feedback circuit formed by the electron-discharge device 14 and the amplifier circuit means i5 from the circuit capacitance represented by the condenser C for minimizing undesired high-frequency phase shift introduced thereby which tends to cause this closed loop feed-baci'. circuit to undergo high-frequency oscillations. This first impedance means may include, for example, a resistor R1 connected in series with an inductauce coil L, for isolating the closed loop feed-backcircuit from the circuit capacitance C. As is apparent from the drawing, resistor R1 and inductance coil L1 constitute a part of the compensating network For producing the desired isolation, this first impedance means is connected in series between the output terminal 21 of the voltage-regulator circuit and a point c: `common to one of the other electrodes, for example the cathode 1o of the elect i-discharge device 14, and the input to the amplifier circuit means 15.

Lastly, the voltage-regulator circuit of -Fig. 2 includes second impedance means for by-passing the first impedance means represented by therresistor R1 and the engagea Operation of voltage-regulator circuit 0f Fig. 2

Considering the operation of the series-type voltageregulator circuit of Fig. 2 just described, this voltageregulator circuit, except for the presence and effect of the compensating network 30, operates in the same manner as the conventional voltage-regulator circuit of Fig. l for supplying a constant magnitude direct-current voltage to the load 13. As mentioned in connection with the conventional voltage-regulator circuit of Fig. 1, such circuit tends to oscillate due to the undesirable high-freA quency phase shift produced by the circuit capacitance represented by the condenser C. Such high-frequency oscillations may be started or triggered, for example, by the high-frequency components of electrical noise which is always present to some degree in all physical circuits. In the voltage-regulator circuit of Fig. 2, which is constructed in accordance with the present invention, such tendency of the regulator circuit to oscillate is either eliminated or considerably reduced by the action of the impedance elements of the compensating network 30.

A key element of the compensating network 3i is the resistor R1 which serves to isolate the closed loop feedback circuit formed by the amplifier and the tube 14 from the circuit capacitance represented by the by-pass condenser C for minimizing the undesired high-frequency phase shift introduced around the feedback circuit by such circuit capacitance. The operation of this isolating resistor R1 may be better understood by referring to Figs. 2a and 2b, Fig. 2a being an alternating-current equivalent circuit diagram for the voltage-regulator circuit of Fig. 2 while Fig. 2b is a vector diagram which illustrates the phase relationships of the various voltages developed around the feed-back loop. As before, the equivalent resistor R represents the variable conductivity of the tube 14 while the resistor ZL represents the equivalent impedance of the load 13. More precisely, Fig. 2a represents the equivalent circuit diagram for the highfrequency signal variations only, as will subsequently become apparent.

Considering a current flowing around the feed-back path including the resistor R, the resistor R1, and the condenser C of the Fig. 2a circuit, it will be apparent that the voltage drop VR1 across the resistor R1 combines with the 90 out-of-phase voltage drop VC across the condenser C to form a voltage signal Vx which is fed back to the input of the amplifier 15. The voltage signal at the output terminals of the amplifier 15, on the other hand, is the vector resultant of the input voltage Vx and the voltage drop VR across the resistor R. This resultant is denoted by the symbol VT. As will be apparent from the vector diagram of Fig. 2b, the voltage VX supplied back to the input of the amplifier 15 is out of phase by an angle 0 with the output voltage VT. It will also be apparent, however, by comparing Fig. 2b with Fig. 1b, that the phase shift around the feed-back path is not as great in the Fig. 2b case. This is because the resistor R1 serves to isolate the effect of the circuit capacitance C from the feed-back circuit formed by the equivalent resistor R and the amplifier 1S. As a result, the phase shift 0 around the feed-back path is minimized to such an extent that the voltage-regulator circuit will not oscillate.

The inductance of coil L1 is effective at frequencies higher than the former self-oscillation frequency of the regulator circuit for producing a leading phase shift which may be utilized to partially compensate for the lagging phase shift normally produced by the internal amplifier stages of the amplifier 15. For simplicity, this coil L1 has not been shown on the equivalent circuit diagram of Fig. 2a.

Because the resistor R1 isolates the amplifier 15 from the output terminal 21, the output impedance of the regulator circuits at low frequencies is increased by approximately the value of R1. The resistance of the resistor R1, even though it may be small, can thus be too great for the direct-current and lower frequency components drawn by the load 13. This is especially true where the load 13 draws rather heavy currents, in which case the voltage drop across even a small value of resistance is rather large. Accordingly, the compensating network 3i) includes second impedance means for lay-passing the isolating resistor R1 for the lower frequency and direct-current components of the current variations drawn by the load. This second impedance means includes the resistor R2 which serves to make a direct connection to the output terminal 21 of the voltage-regulator circuit and the coupling condenser C2 which serves to shift the effective connection of the amplifier 15 input from the output terminal 21 to the cathode 16 of the tube 14 as the frequency is increased. In other words, for direct-current and low-frequency components, the reactance of the condenser C2 is high compared to the resistance of the resistor R2. As a result, therefore, the input of the amplier 15 is effectively connected to and is responsive to the voltage variations at the output terminal 21. For these low-frequency components, then, the voltage-regulator circuit acts like the conventional voltage-regulator circuit of Fig. 1. As the frequency is increased, however, the reactance of condenser C2 decreases until, for the high-frequency components, the reactance thereof is negligible compared to the resistance of the resistor R2. In this condition, the input of the amplifier 15 is effectively connected to the cathodev 16 of the tube 14 and, hence, the resistor R1 is effective to isolate the feed-back circuit formed by the amplifier 15 and the tube 14 from the by-pass condenser C. As a result of this shifting action, self-oscillation of the voltageregulator circuit is prevented for the higher frequency components while the conventional and more sensitive operation of the voltage-regulator circuit is effected for the lower frequency components. The presence of the isolating resistor R1 at the higher frequencies is not objectionable as far as its effect on the output impedance of the regulator circuit is concerned because at `these higher frequencies the reactance of the by-pass condenser C is small enough to maintain a very low output impedance.

' While applicant does not intend to limit the invention to any particular design constants, the following values are representative for the elements of the compensating network 30 of the voltage-regulator circuit of Fig. 2, it being understood that the exact values of these components are dependent on the design of the amplifier 15 and the value of the by-pass condenser C:

Condenser C2 micrornicrofarads 470 Inductance coil L1 microhenrys 0.3 Resistor R1 ohms 0.5 Resistor R2 do 18,000

Description and operation of Fig. 3 voltage-regulator circuit Referring now to Fig. 3 of the drawings, there is shown a shunt-type voltage-regulator circuit designed in accordance with the present invention. This voltage-regulator circuit of Fig. 3 is similar to the series-type regulator of Fig. 2 except that the regulator tube 14 is connected in shunt across the output terminals of the filter 12, which terminals are also connected directly to the output terminals 21, 22 of the voltage-regulator circuit. The regulating action in this case is produced by the loading of the current flow through the shunt-regulator tube v1.4 on the filter 12. In other words, assuming, for example, that the output voltage at the output terminals 21, 22 increases, then, by way of the amplifier 15, this increase is effective to increase the voltage signal supplied to thecontrol electrode 17 of the tube i4 thereby increasing the current drawn by the tube I4. This, in turn, causes an increase in the voltage drop across the internal resistance of the filter 12 thereby decreasing the output voltage back to the desired constant value.

The operation of the compensating network 30 of the Fig. 3 regulator circuit in preventing self-oscillation of the closed loop feed-back circuit formed by the amplier I5 and the tube i4 is similar to the operation of the corresponding network in the Fig. 2 regulator circuit. In other words, the resistor R1 serves to isolate the feed-back circuit formed by the amplifier i5 and the tube 14 from the circuit capacitance represented by the condenserC. Similarly, the variation of the reactance of the condenser C2 with frequency serves to shift the amplifier 15 input from the .output terminal 21 to the anode i9 of the tube 14, thereby to allow conventional operation of the voltage-regulator -circuit for the direct-current and lower frequency components or any current variations drawn by the load 13. The alternating-current equivalent circuit diagram of Fig. 2a may also be taken as referring to the Fig. 3 voltage-regulator circuit, provided the equivalent resistor R is understood to represent the control electrode i7 to anode i9 conductance of the tube 14.

Compensaling network of Fig. 4

Referring now to Fig. 4 of the drawings, there is shown an alternative form of compensating network 30 which may be utilized in place of the compensating network 3@ of .either the Fig. 2 or Fig. 3 voltage-regulator circuits. In use, the terminals rz, b, and d of the network 30' are connected to the same points as the correspondingly designated terminals'of the network 30 of either Fig. 2 or Fig. 3.

In operation the resistor R1 and the inductance coil L1 serve to isolate the feed-back circuit of the voltage regulator from the circuit capacitance across the output terminals thereof in the same manner as previously mentioned. The Fig. 4 network differs from that previously mentioned in `that a .second inductance coil L2 is coupled across the isolating resistor R1 and serves to by-pass this resistor for the direct-.current and low-frequency components of any currentvariations drawn by the load. This is feasible because the reactance of the inductance coiiV L2 is negligible for the low-frequency components and increases as the frequency is increased. For frequencies where the reactance of the inductance coil L2 becomes greater than the resistance of the resistor R1, the inductance coil L2 is, in effect, no longer in the circuit thus allowing the resistor R1 to perform the desired function of isolation. Y s From the foregoing description of the various embodiments of the invention it will be apparent that a voltage regulator constructed in accordance with the invention represents a new and improved voltage-regulator circuit which is capable of having a high degree of direct-current stability and which is not readily susceptible to self-oscillation.

`While there have been Vdescribed what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as tall within the true spirit and scope of the invention.

Whatis claimed is:

l. A voltage-regulator circuit for supplying a constant Vmagnitude direct-current voltage to a load and normally having circuit capacitance coupled across the output terminals thereof which tends to cause the voltv Ui age-regulator circuit to oscillate, the voltage-regulator circuit comprising: supply circuit means for supplying a direct-current voltage; an electron-discharge device for adjusting the magnitude of the direct-current voltage supplied to the load; amplifier circuit means responsive to variations 'in the magnitude of the voltage supplied to the load for controlling the operation of the electron-discharge device to compensate for such voltage variations; first impedance means for isolating the closed loop feedback circuit formed by the electron-discharge device and the amplifier circuit means from the circuit capacitance for minimizing undesired high-frequency phase shift introduced thereby which tends to cause this closed loop feed-back circuit to undergo high-frequency oscil` lations; and Second impedance means for by-passing the first impedance means for enabling normal operation of the voltage-regulator circuit for the lower frequency components of the load current variations.

2. A voltage-regulator circuit for supplying a constant magnitude direct-current voltage to a load and normally having circuit capacitance coupled across the output terminals thereof which tends to cause the voltage-regulator circuit to oscillate, the voltage-regulator circuit comprising: supply circuit means for supplying a direct-current voltage; an electron-discharge device for adjusting the magnitude of the direct-current voltage supplied to the load; amplifier circuit means responsive to variations in the magnitude ofthe voltage supplied to the load for controlling the operation of the electrondischarge device to compensate for such voltage variations; first impedance means including a resistor for isolating the closed loop feed-back circuit formed by the electron-discharge device and the amplifier circuit means from the circuit capacitance for minimizing undesired high-frequency phase shift introduced thereby which tends to cause this closed loop feed-back circuit to undergo high-frequency oscillations; and second irnpedance means for by-passing the first impedance means for enabling normal operation of the voltage-regulator circuit for the lower frequency components of the load current variations.

3. A voltage-regulator circuit for supplying a constant magnitude direct-current voltage to a load and normally having circuit capacitance coupled across the output terminals thereof which tends to cause the voltage-regulator circuit to oscillate, the voltage-regulator circuit comprising: supply circuit means for supplying a direct-current voltage; an electron-discharge device for adjusting the magnitude of the direct-current voltage supplied to the load; amplifier circuit means responsive to variations in the magnitude of the voltage supplied to the load for controlling the operation of the electrondischarge device to compensate for such voltage variations; first impedance means including a resistor con Y nected in series with an inductance coil for isolating the closed loop feed-back circuit formed by theelectron-discharge device and the amplifier circuit means from the circuit capacitance for minimizing undesired highfrequency phase shift introduced thereby which tends to cause this closed loop feed-back circuit to undergo high-frequency oscillations; and second impedance means for lay-passing the first impedance means for enabling normal operation of the voltage-regulator circuit for the lower frequency components of the load current variations.

4. A voltage-regulator circuit for supplying a constant magnitude `direct-current voltage to a load and normally having circuit capacitance coupled across the output terminals thereof which tends to cause the voltage-regulator circuit to oscillate, the voltage-regulator circuit comprising: supply circuit means for supplying a direct-current voltage; an electron-discharge device for adjusting the magnitude of the direct-current voltage supplied to the load; amplier circuit means responsive to variations in the magnitude of the voltage supplied to the load for controlling the operation of the electrondischarge device to compensate for such voltage variations; first impedance means for isolating the closed loop feed-back circuit formed by the electron-discharge device and the ampliier circuit means from the circuit capacitance for minimizing undesired high-frequency phase shift introduced thereby which tends to cause this closed loop feed-back circuit to undergo high-frequency oscillations, and second impedance means including a by-pass resistor and a condenser for enabling the resistor to by-pass the first impedance means for enabling normal operation of the voltage-regulator circuit for the lower frequency components of the load current variations.

5. A voltage-regulator circuit for supplying a snstant magnitude direct-current voltage to a load and normally having circuit capacitance coupled across the output terminals thereof which tends to cause the voltageregulator circuit to oscillate, the voltage-regulator circuit comprising: supply circuit means for supplying a vdirect-current voltage; an electron-discharge device having `a cathode, a control electrode, land an anode for adjusting the magnitude of the `direct-current voltage supplied to the load; amplifier circuit means coupled to the control electrode 4of the electron-discharge device and responsive to variations in the magnitude of the voltage supplied to the load for controlling the conductivity of the electron-discharge device to compensate for such voltage variations; lirst impedance means connected 'n eries ybetween one of the output terminals of the voltage-regulator circuit and a point common to one of the other electrodes of the electron-discharge device and the input to the amplifier circuit means for isolating the closed loop feed-back circuit formed by the electrondischarge device and the lampliiier circuit means from the circuit capacitance for minimizing undesired highfrequency phase shift introduced thereby which tends to cause Ithis closed loop feed-back circuit to undergo highfrequency oscillations; and second impedance means for lay-passing the first impedance means for enabling normal operation of the voltage-regulator circuit for the lower frequency components of the load current variations.

6. A series-type voltage regulator circuit for supplying a constant magnitude direct-current voltage to a load and normally having circuit capacitance coupled across the pair of output terminals thereof which tends to cause the voltage-regulator circuit to oscillate, the voltageregulator circuit comprising: supply circuit means for supplying a direct-current voltage; an electron-discharge device having a cathode, a control electrode, and an anode the anode-to-cathode dischar-ge path of the device being coupled in series between the supply circuit means and a first one of the output terminals of the voltage-regulator circuit for adjusting the magnitude of the direct-current voltage supplied to the load; amplifier circuit means coupled between the control electrode of the electron-discharge device and the mentioned first output terminal and responsive to variations in the magnitude of the voltage supplied to the load for controlling the conductivity of the electron-discharge `device to compensate for such voltage variations; first impedance means including a resistor connected in series in the path between the mentioned first output terminal of the voltageregulator circuit and a point common to the output electrode of the electron-discharge device and the input to the amplifier circuit means for isolating the closed loop feed-back circuit formed by thhe electron-discharge device and the amplifier circuit means from the circuit capacitance for minimizing undesired high-frequency phase shift introduced thereby which tends to cause this closed loop feed-back circuit to undergo high frequency oscil.- lations; and second impedance means for lay-passing the first impedance means for enabling normal operation of `the voltage-regulator circuit for the lower frequency components of the load current variations.

7. A shunt-type voltage-regulator circuit for supplying a constant magnitude direct-current voltage to a load and normally Ihaving circuit capacitance `coupled across the pair of output terminals thereof which tends to cause the voltage-regulator circuit to oscillate, the voltage-regulator circuit comprising: supply circuit means for supplying a `direct-current voltage to the output terminals of the voltage-regulator circuit; an electron-discharge device having a cathode, a control electrode, and an anode, the anode-to-cathode discharge path of the device being coupled across the output terminals of the voltage-regulator circuit for adjusting the magnitude of the directv current voltage supplied to the load by adjusting the loading on the `supply circuit means; amplifier circuit means coupled between the control electrode and the anode of the electron-discharge device and responsive to variations in the magnitude of the voltage supplied -to the load for controlling the conductivity of the electrondischarge device 4to compensate for such voltage variations; first impedance means including a resistor connected in series in the path between the anode of the electron-discharge device and the corresponding output terminal of the voltage-regulator circuit for isolating the closed loop feedback circuit formed by the electrondischarge device and the amplifier circuit means from the circuit capacitance for minimizing undesired highfrequency phase shift introduced thereby which tends to cause this closed loop feed-back circuit to undergo highfrequency oscillations; and second impedance means for by-passing the first impedance means for enabling normal operation of the voltage-regulator circuit for the lower frequency components of the load current variations.

References Cited in the file of this patent UNITED STATES PATENTS 2,594,006 Friend Apr. 22, 1952 

